Root resorption and tooth movement in orthodontically treated, calcium-deficient, and lactating rats

[Accelerated tooth movement by alveolar corticotomy or piezocision]

The relatively recent introduction of corticotomies and piezocision has made it possible for orthodontists to accelerate tooth movement and thereby to shorten the length of orthodontic treatment. Specialists emphasizing a mechanistic concept have been debating the underlying basic biological mechanics of these new therapeutic tools with opposing specialists who support a biological conception. Our analysis of different publications on the subject suggests that the biological explanation, with its emphasis on the Regional Acceleratory Phenomenon (RAP), is correct. However, the majority of studies in this field are not based on the principle of evidence based medicine (EBM).

Association between root resorption incident to orthodontic treatment and treatment factors

The purpose of this study was to clarify the prevalence and degree of root resorption induced by orthodontic treatment in association with treatment factors. The files of 243 patients (72 males and 171 females) aged 9-51 years were randomly selected from subjects treated with multi-bracket appliances. The severity of root resorption was classified into five categories on radiographs taken before and after treatment. The subjects were divided into extraction (n = 113 patients, 2805 teeth) and non-extraction (n = 130 patients, 3616 teeth) groups and surgical (n = 56 patients, 1503 teeth) and non-surgical treatment (n = 187 patients, 4918 teeth) groups. These subjects were also divided into two or three groups based on the duration of multiloop edgewise archwire (MEAW) treatment, elastic use, and total treatment time: 0 month (T1; n = 184 patients, 4831 teeth), range 1-6 months (T2; n = 37 patients, 994 teeth), more than 6 months (T3; n = 22 patients, 596 teeth); range 0-6 months (n = 114 patients, 3016 teeth) more than 6 months (n = 129 patients, 3405 teeth); range 1-30 months (n = 148 patients, 3913 teeth) and more than 30 months (n = 95 patients, 2508 teeth). The prevalence of overall and severe root resorption evaluated by the number of subjects and teeth was compared with a chi-square test. A Student's t-test for unpaired data was used to determine any statistically significant differences. The prevalence of severe root resorption based on the number of teeth was significantly higher in the group with extractions (P < 0.01). Longer use of a MEAW appliance and elastics also produced a significantly higher prevalence of root resorption (P < 0.05). On the other hand, the prevalence of severe root resorption was not significantly different between the subjects treated with or without surgery, but there was a significant increase when treatment time was prolonged (P < 0.05). A significant difference was found in the amount of root movement of the upper central incisors and the distance from their root apices to the cortical bone surface (P < 0.05). These are regarded as essential factors in the onset of root resorption. These results indicate that orthodontic treatment with extractions, long-term use of a MEAW appliance and elastics, treatment time, and distance of tooth movement are risk factors for severe root resorption.

Dentoalveolar transport osteodistraction and canine distalization

The orthodontic treatment period with extractions is prolonged in many cases because of the limited rate of biological tooth movement. An approach using transport distraction osteogenesis was designed to reduce orthodontic and orthognathic treatment time. Overall management of selected alveolar cleft cases with wide defects may also be optimized and simplified through transport distraction of a tooth-bone segment. We will discuss our experience with 73 cases, both conventional orthodontic cases and orthognathic patients, in which dentoalveolar distraction was used to reduce orthodontic treatment time and to treat wide alveolar clefts with compromised soft tissues to facilitate optimal outcome.

Orthodontic treatment of an anterior openbite with the aid of corticotomy procedure: Case report

This case report illustrates the orthodontic treatment combined with the corticotomy technique in an adult patient to accelerate tooth movement and shorten the treatment time. The patient was a 22-year-old woman with an anterior open bite and flared and spaced upper and lower incisors. First, fixed orthodontic appliances (bidimensional edgewise brackets) were bonded, and a week later buccal and lingual corticotomy with alveolar augmentation procedure in the maxillary arch from the first molar to the contralateral first molar, and from canine to canine in the mandibular arch was performed. Orthodontic therapy proceeded with frequent activation of the appliances to retract the incisors every 2 weeks. The total treatment time was 5 months and no adverse effects were observed at the end of active treatment. The addition of the decortication procedure to the conventional orthodontic therapy decreased the duration of treatment significantly. Successful closure of the anterior open bite with adequate overbite and interdigitation of the teeth were achieved.

Corticotomy-assisted orthodontic treatment: review

Corticotomy-assisted orthodontic treatment is an established and efficient orthodontic technique that has recently been studied in a number of publications. It has gradually gained popularity as an adjunct treatment option for the orthodontic treatment of adults. It involves selective alveolar decortication in the form of decortication lines and dots performed around the teeth that are to be moved. It is done to induce a state of increased tissue turnover and a transient osteopenia, which is followed by a faster rate of orthodontic tooth movement. This technique has several advantages, including faster tooth movement, shorter treatment time, safer expansion of constricted arches, enhanced post-orthodontic treatment stability and extended envelope of tooth movement. The aim of this article is to present a comprehensive review of the literature, including historical background, contemporary clinical techniques, indications, contraindications, complications and side effects.

Apical root resorption in orthodontic patients with en-masse maxillary anterior retraction and intrusion with miniscrews

INTRODUCTION

The purposes of this retrospective study were to investigate the apical root resorption of maxillary incisors in orthodontic patients with en-masse maxillary anterior retraction and intrusion with miniscrews and the factors disposing a patient to apical root resorption.

METHODS

Fifty adult patients with maxillary protrusion were included; 30 were treated with miniscrews and extraction of the maxillary first premolars (group I), and 20 were treated with extraction of the maxillary first premolars (group II). For each patient, periapical films of the maxillary incisors and lateral cephalometric radiographs were taken before and after treatment to evaluate apical root resorption and cephalometric measurements. The intergroup differences were analyzed with the Student t test and the correlations between apical root resorption and cephalometric measurements were analyzed by the Pearson correlation.

RESULTS

The apical root resorption values were 16.0% to 20.0% (2.5-2.8 mm) in group I and 13.4% to 14.4% (2.1-2.3 mm) of the original root length in group II. Group I had significantly more severe Class II jaw discrepancy (ANB, 7.1 degrees +/- 1.9 degrees ) than did group II (ANB, 3.2 degrees +/- 2.9 degrees ). The amount of maxillary en-masse anterior retraction (8.2 +/- 2.4 mm), the duration of treatment (28.3 +/- 7.3 months), and apical root resorption of maxillary lateral incisors were significantly greater in group I than in group II. Apical root resorption of the maxillary central incisors was significantly correlated to the duration of treatment but not to the amount of en-masse retraction, intrusion, or palatal tipping of maxillary incisors.

CONCLUSIONS

Miniscrew anchorage allows for more maxillary en-masse anterior retraction in patients with severe Class II cases. But the time needed for the greater amount of maxillary en-masse anterior retraction with miniscrew anchorage is longer and might dispose the patient to more apical root resorption.

Assessment of trabecular pattern on periapical and panoramic radiographs: a pilot study

OBJECTIVE

This methodological study aimed to determine whether the mandibular trabecular bone assessment from panoramic radiographs, using a visual index, corresponds to the evaluation obtained from periapical radiographs.

MATERIAL AND METHODS

A panoramic radiograph and corresponding periapical radiographs of the region of the lower premolars and molars were collected from each of 32 patients (mean age 18.5 +/- 5.5 years). Two calibrated observers assessed randomly the interdental sites between the first molar and second premolar and between the two premolars on all the radiographs using a visual index. Evaluations were repeated with an interval of 60 days. The results of the repeated evaluations were used to assess intra- and inter-observer agreements, employing Kappa statistics. Spearman's correlation was used to determine the association between assessments of panoramic and periapical radiographs.

RESULTS

In total, 79 interdental sites were evaluated on the panoramic and periapical radiographs. The visual analysis of periapical radiographs revealed intra-observer agreements of 0.88 for observer 1 and 0.93 for observer 2, and an inter-observer agreement of 0.82. The intra-observer agreement for panoramic radiographs was 0.79 and 0.83 for observers 1 and 2, respectively, and the inter-observer agreement was 0.79. A substantial correlation was found between periapical and panoramic radiographs (rho = 0.737, p = 0.001).

CONCLUSIONS

Although panoramic radiographs are less reliable than periapical radiographs, they can be used for assessment of the trabecular bone pattern with the aid of a visual index. Training on the method is recommended to obtain results with a high reproducibility.

Biologic response of rapid tooth movement with periodontal ligament distraction

INTRODUCTION

Length of treatment is a complaint of many orthodontic patients. The purpose of this study was to evaluate the security and feasibility of rapid tooth movement with periodontal ligament distraction.

METHODS

Eight male beagles, aged 13 to 16 months, were used in this study. Extraction of the mandibular second premolar and alveolar surgery to reduce the osteal resistance on the mesial side of the extraction socket were performed on the experimental side. Then a device was placed to distract the first premolars distally on the experimental side; on the control side, the first premolars were distalized with nickel-titanium coil springs. The beagles were killed in the first, second, fourth, and eighth weeks after orthodontic force application.

RESULTS

The first premolar on the experimental side moved more rapidly than that on the control side (P <0.05). Histologic data indicated that more new bone was deposited on tension area of the experimental side than on the control side. Active and extensive bone resorption in the compressive area and bone deposition in the tension area were observed on the experimental side.

CONCLUSIONS

These results suggest that the periodontal ligament can be rapidly distracted without complications. The rapid orthodontic tooth movement by distracting the periodontal ligament cannot be emulated by current conventional orthodontic concepts and methods.

Effects of Corticision on paradental remodeling in orthodontic tooth movement

OBJECTIVE

To investigate the biologic effects of Corticision on alveolar remodeling in orthodontic tooth movement.

MATERIALS AND METHODS

In this study, 16 cats were divided into 3 groups: group A, only orthodontic force (control); group B, orthodontic force plus Corticision; and group C, orthodontic force plus Corticision and periodic mobilization. Histologic and histomorphometric studies were performed on tissue specimens on days 7, 14, 21, and 28.

RESULTS

Extensive direct resorption of bundle bone with less hyalinization and more rapid removal of hyalinized tissue were observed in group B. The accumulated mean apposition area of new bone on day 28 was observed to be 3.5-fold higher in group B than in the control group A.

CONCLUSIONS

Corticision might be an efficient procedure for accelerating orthodontic tooth movement accompanied with alveolar bone remodeling.

Medication effects on the rate of orthodontic tooth movement: a systematic literature review

INTRODUCTION

Recently, several reviews have been published on the effects of medications on bone physiology and the clinical side effects in orthodontics. However, the effects of medications on the rate of orthodontic tooth movement have not been evaluated.

METHODS

A systematic literature review on the effects of medications and dietary supplements on the rate of experimental tooth movement was performed by using PubMed (1953-Oct 2007), Web of Science, and Biosis, complemented by a hand search.

RESULTS

Forty-nine articles were included in the review, but their interpretation was hindered by the variability in experimental design, magnitude of force applied during tooth movement, and medication regimens. Therapeutic administration of eicosanoids resulted in increased tooth movement, whereas their blocking led to a decrease. Nonsteroidal anti-inflammatory drugs (NSAIDs) decreased tooth movement, but non-NSAID analgesics, such as paracetamol (acetaminophen), had no effect. Corticosteroid hormones, parathyroid hormone, and thyroxin have all been shown to increase tooth movement. Estrogens probably reduce tooth movement, although no direct evidence is available. Vitamin D3 stimulates tooth movement, and dietary calcium seemed to reduce it. Bisphosphonates had a strong inhibitory effect.

CONCLUSIONS

Medications might have an important influence on the rate of tooth movement, and information on their consumption is essential to adequately discuss treatment planning with patients.

Modeling of trabecular bone and lamina dura following selective alveolar decortication in rats

BACKGROUND

Modifying the balance between resorption and apposition through selectively injuring the cortical plate of the alveolus has been an approach to speed tooth movement and is referred to as periodontally accelerated osteogenic orthodontics. The aim of this study was to investigate the alveolar response to corticotomy as a function of time and proximity to the surgical injury in a rat model.

METHODS

Maxillary buccal and lingual cortical plates were injured in 36 healthy adult rats adjacent to the upper left first molars. Twenty-four animals were euthanized at 3, 7, or 11 weeks. In one group, the maxillae were removed and stripped of soft tissues, and histomorphometric analysis was performed to study alveolar spongiosa and periodontal ligament (PDL) modeling dynamics. Catabolic activity was analyzed with tartrate-resistant acid phosphatase-positive osteoclasts and preosteoclasts. Anabolic actions were measured using a fluorescent vital bone stain series followed by sacrifice at 30 and 51 days. To further analyze the new bone formation, a separate group of animals were fed with calcein fluorescent stain and processed for non-decalcified fluorescent stain histology.

RESULTS

At 3 weeks, the surgery group had significantly (P <0.05) less calcified spongiosa bone surface, greater periodontal ligament surface, higher osteoclast number, and greater lamina dura apposition width. The catabolic activity (osteoclast count) and anabolic activity (apposition rate) were three-fold greater, calcified spongiosa decreased by two-fold, and PDL surface increased by two-fold. Surgical injury to the alveolus that induced a significant increase in tissue turnover by week 3 dissipated to a steady state by postoperative week 11. The impact of the injury was localized to the area immediately adjacent to the decortication injury.

CONCLUSION

Selective alveolar decortication induced increased turnover of alveolar spongiosa, and the activity was localized; dramatic escalation of demineralization-remineralization dynamics is the likely biologic mechanism underlying rapid tooth movement following selective alveolar decortication.

[Alveolar osteotomy and rapid orthodontic treatments]

When combined with orthodontics, selective periodontal decortication has been shown to be clinically effective in eliminating severe malocclusions three to four times more rapidly than conventional orthodontic treatment. Our technique combines surgical scarring of the cortical bone on both labial and lingual sides of the teeth to be moved, with an augmentation graft to increase alveolar volume. Alveolar spongiosa undergoes rapid transformation as the body attempts to heal the wounds to the cortices resulting in marked tissue turnover. The patient is seen every two weeks and most cases are completed within six months of orthodontic treatment. Moreover, this technique significantly expands the scope of treatment in resolving many skeletal problems such as openbites and severe maxillary constrictions, conditions typically relegated to orthognathic surgery. Clinical outcomes research has shown that the immediate post treatment results settle better during retention and that the long term results become more stable. These facts are likely due to the high tissue turnover induced by decortication as well as the thicker cortical bone resulting from the augmentation grafting.

Acceleration of orthodontic tooth movement by alveolar corticotomy in the dog

INTRODUCTION

Tooth movement and alveolar bone reaction after corticotomies have not been thoroughly examined. In this study, the effects of corticotomies on orthodontic tooth movement and alveolar bone reaction were investigated in dogs.

METHODS

Corticotomies were performed on the cortical bone of the mandibular left third premolar region in 12 male adult beagles. The third premolars on the left experimental side and on the right sham side were moved mesially with a continuous force of 0.5 N.

RESULTS

Tooth movement velocities from 0 to 1 week and from 1 to 2 weeks after the corticotomies were significantly faster on the experimental side than on the sham side. Hyalinization of the periodontal ligament appeared only at 1 week after the corticotomies on the experimental sides, whereas it was observed from 1 to 4 weeks after the corticotomies on the sham sides. Tartrate-resistant-acid-phosphatase positive cells of the experimental side tended to work vigorously at an early time on the alveolar wall and in the bone marrow cavities.

CONCLUSIONS

Orthodontic tooth movement increased for at least 2 weeks after the corticotomies. This might be brought about by rapid alveolar bone reaction in the bone marrow cavities, which leads to less hyalinization of the periodontal ligament on the alveolar wall.

Rapid orthodontic tooth movement aided by alveolar surgery in beagles

INTRODUCTION

It has been reported that oral surgery can accelerate orthodontic tooth movement. The purpose of this study was to evaluate the effects of alveolar surgery that undermines interseptal bone in orthodontic tooth movement.

METHODS

Ten male beagles, aged 12 to 15 months, were used in this study. Extraction of the mandibular second premolar and alveolar surgery to reduce the osteal resistance on the mesial side of the extraction socket were performed on the experimental side; on the control side, only the second premolar was extracted. The first premolars were distalized against the third premolars with orthodontic nickel-titanium coil springs on the both sides. The beagles were killed in the first, second, third, fourth, and eighth weeks after orthodontic force application.

RESULTS

The first premolar on the experimental side moved more rapidly than that on the control side (P <.01). Tissue slices were obtained for histological evaluation. No obvious root resorption and no irreversible injury to the pulp were observed on either side. Active and extensive bone resorption in the compressive area and bone deposition in the tension area were observed on the experimental sides.

CONCLUSIONS

Self-fluorescence checks showed that more new bone was deposited in the tension area of the experimental side than on the control side (P <.05). These results suggest that alveolar surgery might be an effective and safe way to aid orthodontic tooth movement.

Physical properties of root cementum: Part 9. Effect of systemic fluoride intake on root resorption in rats

INTRODUCTION

Orthodontically induced inflammatory root resorption is a common complication in orthodontic treatment. Fluoride has been reported to have a beneficial effect against root resorption in dental traumatology. The effect of fluoride on orthodontically induced inflammatory root resorption has not been investigated. This study was undertaken to investigate the effect of fluoride on the incidence of root resorption.

METHODS

Thirty-two female 8-week-old Wistar rats were separated into 4 groups. Two groups (6 rats per group) were controls; they did not undergo orthodontic tooth movement. The other 2 groups (10 rats per group) had orthodontic tooth movement consisting of activated 100-g closing nickel-titanium coils (NiTi 10-000-06, GAC International, Bohemia, NY) connecting the mandibular first molar to the incisors. Fluoridated water (100 ppm) was given ad libitum to 1 control and 1 experimental group. The other 2 groups received deionized water. After 2 weeks, the animals were killed, and the samples were harvested. Resorption craters were scanned with a Micro CT (SkyScan 1072, Aartselaar, Belgium). Software analysis of the scanned samples provided a volumetric measurement of the resorption craters on the mandibular molar cementum surface.

RESULTS

Resorption sites were found in the control samples, especially on the distal surfaces; this could be attributed to normal physiological tooth drift. Resorption sites were significantly (P <.05) increased in the groups receiving orthodontic tooth movement.

CONCLUSIONS

Fluoride reduces the size of resorption craters, but the effect is variable and not statistically significant (P >.05).

An adult bimaxillary protrusion treated with corticotomy-facilitated orthodontics and titanium miniplates

We performed an orthodontic treatment combined with corticotomy and the placement of titanium miniplates in an adult patient who desired a shortened treatment period. The patient had an Angle Class I malocclusion with flaring of the maxillary and mandibular incisors. First, titanium miniplates were placed into the buccal alveolar bone of the maxilla for absolute orthodontic anchorage. Second, an edgewise appliance was applied to the maxillary and mandibular teeth. Then, the maxillary first premolars and mandibular second premolars were extracted. At the same time, a corticotomy was performed on the cortical bone of the lingual and buccal sides in the maxillary anterior as well as the mandibular anterior and posterior regions. Leveling was initiated immediately after the corticotomy. The extraction spaces were closed with conventional orthodontic force (approximately 1 N per side). The edgewise appliance was adjusted once every 2 weeks. The total treatment time was 1 year. Cephalometric superimpositions showed no anchorage loss, and panoramic radiographs showed neither significant reduction in the crest bone height nor marked apical root resorption. A corticotomy-facilitated orthodontic treatment with titanium miniplates might shorten an orthodontic treatment period without any anchorage loss or adverse effects.

Changes in the radiographic characteristics of the mandibular alveolar process in dentate women with varying bone mineral density: a 5-year prospective study

The association between skeletal bone mineral density (BMD) and mandibular alveolar bone mass has been reported to be rather weak, probably due to local functional factors. Many new investigations are therefore focused on assessing the mandibular bone structure. No long-term structural alterations have been reported in human mandibular bone with the exception of alveolar crest changes related to periodontal disease. The aim of this prospective study was to investigate dentate women to see if possible alterations in the radiographic characteristics of the mandibular alveolar bone are related to changes in BMD. The BMD of 131 women (initial age 22-75 years) was determined in the distal forearm with dual energy X-ray absorptiometry on two occasions separated by an interval of 5 years. Mandibular alveolar bone mass (MABM) was assessed both by the optical density and by the grey-level value on digitized, calibrated, periapical radiographs. The radiographic alveolar bone structure was evaluated with a visual index [Lindh C, Petersson A, Rohlin M. Assessment of the trabecular pattern before endosseous implant treatment: diagnostic outcome of periapical radiography in the mandible. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;82:335-43. ] and digitally by the alveolar bone texture. MABM decreased significantly during the 5-year period. Changes in MABM, evaluated by the mean grey-level value of a bone segment between the premolars, were correlated to changes in skeletal BMD (r = 0.33, P < 0.001). Changes in MABM, evaluated by the optical density, did not correlate to changes in skeletal BMD. The overall trabecular pattern did not change during the study period, but small changes in the bone texture were measured. The changes in the bone texture were correlated with BMD change (r = 0.39, P < 0.001). We conclude that changes in the mandibular alveolar bone do reflect changes in the skeletal BMD, and these may be estimated on periapical radiographs by changes in their grey-level value and their texture.

Physical properties of root cementum: Part 6. A comparative quantitative analysis of the mineral composition of human premolar cementum after the application of orthodontic forces

INTRODUCTION

The aim of this study was to examine quantitatively with electron probe microanalysis (EPMA) the calcium (Ca), phosphorus (P), and fluoride (F) concentrations in human first premolar cementum after the application of light and heavy orthodontic forces.

METHODS

Thirty-six maxillary and mandibular first premolars (18 experimental, 18 control) were extracted from 16 subjects (10 male, 6 female; mean age, 13.9 years; range, 11.7-16.1 years) who were randomly assigned to the light-force or the heavy-force group. In the light-force group, 25 g of buccally directed force was applied to the experimental premolar; in the heavy-force group, 225 g of buccally directed force was applied to the experimental premolar. The contralateral premolar served as the control. The experimental and control premolars were extracted 28 or 29 days after initial force application and prepared for EPMA. The Ca, P, and F concentrations were measured on the buccal and lingual surfaces at the midpoint of the cervical, middle, and apical thirds of the root from the outer to the middle to the inner third of the cementum.

RESULTS

Little change was found in the mineral composition of cementum after the application of light forces; however, there was a trend toward an increase in the mineral composition (Ca, P, and F) of cementum at various areas of periodontal ligament compression. The application of heavy forces caused a significant (P = .000) decrease in the Ca concentration of cementum at certain areas of periodontal ligament tension. The application of both light and heavy orthodontic forces did not appear to influence the F concentrations in cementum.

CONCLUSIONS

Heavy orthodontic forces cause alterations in the mineral content of cementum; light forces cause little change.

Influence of steroid drugs on orthodontically induced root resorption

OBJECTIVES

To investigate the effect of acute and chronic corticosteroid treatment on orthodontically induced root resorption.

DESIGN

'Split mouth' design performing orthodontic tooth movement in 64, 6-month-old male rats divided into three groups: acute (n = 22), chronic (n = 23) and control group (n = 19). Acute and chronic group received corticosteroid treatment (8 mg/kg/day) for 3 and 7 weeks, respectively, while no pharmacological treatment was performed in the control group. Performed at the Department of Orthodontics, School of Dentistry, University of Aarhus, Aarhus, Denmark.

EXPERIMENTAL VARIABLE

The upper left first molar was moved mesially for 21 days in all three groups with 25 g of force. Undecalcified histological sections were cut at the coronal and apical level.

OUTCOME MEASURE

The number of intersections hitting resorption lacunae (ES), defined as a scalloped surface with or without cementoclasts, over the total number of intersections hitting the root surface (RS) were recorded and expressed as percentage.

RESULTS

The acute group showed significantly more root resorption at the mesio-coronal level compared with the control and the chronic group.

CONCLUSION

This could be ascribed to the lack of balance between blastic activities (inhibited by the drug) and the clastic activities (enhanced or unchanged by drug administration) occurring in the initial phase of drug administration. As a consequence, a careful monitoring of patients undergoing acute corticosteroid treatment is suggested.

Root resorption associated with orthodontic force in inbred mice: genetic contributions

Root resorption (RR) is an unwanted sequela of orthodontic treatment. Despite rigorous investigation, no single factor or group of factors that directly causes RR has been identified. The purpose of this study was to examine the effect of the genotype on susceptibility or resistance to develop RR secondary to orthodontic force. Nine-week-old male mice from eight inbred strains were used and randomly distributed into control (C) or treatment (T) groups as follows: A/J (C = 9,T = 9), C57BL/6J (C = 7,T = 8), C3H/HeJ (C = 8,T = 6), BALB/cJ (C = 8,T = 6), 129P3/J (C = 6,T = 8), DBA/2J (C = 8,T = 9), SJL/J (C = 8,T = 10), and AKR/J (C = 9,T = 8). Each of the treated mice received an orthodontic appliance to tip the maxillary left first molar mesially for 9 days. Histological sections of the tooth were used to determine RR and tartrate resistant acid phosphatase (TRAP) activity. The Wilcoxon ranked-sum non-parametric test was used to evaluate differences between the groups. The results showed that the DBA/2J, BALB/cJ, and 129P3/J inbred mouse strains are highly susceptible to RR, whereas A/J, C57BL/6J and SJL/J mice are much more resistant. The variation in the severity of RR associated with orthodontic force among different inbred strains of mice when age, gender, food, housing, and orthodontic force magnitude/duration are controlled support the hypothesis that susceptibility or resistance to RR associated with orthodontic force is a genetically influenced trait.

A influência de medicamentos na movimentação ortodôntica: uma análise crítica da literatura

Neste trabalho analisou-se criteriosamente a literatura pertinente sobre a influência de medicamentos na movimentação dentária induzida, avaliando os métodos experimentais para correlacioná-los com a aplicabilidade e extrapolação para a clínica ortodôntica. Devido aos trabalhos experimentais serem feitos em animais, que têm um tempo de vida curto, as doses dos medicamentos são elevadas e os períodos de administração muito longos. Portanto, não se pode afirmar sobre qualquer alteração na movimentação dentária induzida causada por algum tipo de medicamento que o paciente faça uso durante o tratamento ortodôntico.

Maxillary incisor root resorption after rapid palatal expansion in Felis catus

Root resorption after rapid palatal expansion (RPE) treatment was found in anchored teeth but has not been studied on non-anchored incisors. This study evaluated root resorption, root tipping, and root proximity of maxillary incisors after RPE treatment. Fourteen cats were divided into treated (n = 10) and untreated (n = 4) groups. The RPE treatment consisted of active, retention, and relapse phases, lasting 25, 60 and 60 d, respectively. Standardized occlusal radiographs were taken to measure tipping and root proximity before and after each treatment phase. Maxillary incisors were analysed histologically by fluorescent microscopy for root resorption. Data was analysed statistically with anova with repeated measures, t-test and Pearson's coefficient of correlation. Root resorption was confined to the first incisors and was 750-fold greater in the treated vs. the control group. Root tipping and root proximity were significantly greater (2.5- and 17-fold, respectively) in the first than in the second maxillary incisor and highly correlated with root resorption (r = -0.927 and 0.723, respectively). This suggests a cause (tipping and root proximity) and effect (root resorption) relationship. Data suggest that first maxillary incisor susceptibility to root resorption during RPE is associated with severe tipping and root proximity.

Bone structure effect on root resorption

OBJECTIVES

To explore if alveolar bone shape and density might promote external apical root resorption.

SETTING AND SAMPLE POPULATION

Panoramic radiographs of 700 patients who had orthodontic treatment at Temple University were reviewed and 22 patients with radiographic evidence of root resorption on the lower incisors were selected for the study. Exclusion criteria included a history of systemic diseases, craniofacial abnormalities, tooth injury, endodontically treated teeth, and impacted teeth.

METHODS

Pre-treatment (T1) and post-treatment (T2) cephalometric radiographs were converted into digital format and enhanced to reduce contrast variability and improve edge definition. Tooth length, root length, root area, alveolar area around the root including cortical area, area of medullary bone, and area of the symphysis were measured using an interactive software algorithm. A region of interest within the symphysis was also defined and trabecular space area and fractal dimension calculated as an estimate of bone density.

RESULTS

Root area and tooth length were correlated negatively with changes in root area, tooth area, and root length. Larger teeth demonstrated a greater amount of root resorption. Dentoalveolar complex dimensions remained relatively unchanged during tooth movement. The amount of alveolar bone around the root, thickness of cortical bone, density of the trabecular network, and fractal dimension showed no significant correlation with the extent of the external apical root resorption.

CONCLUSIONS

The results of this study suggest that the density and morphology of the dentoalveolar complex are not significant factors in the etiology of external apical root resorption.

Tissue reaction to orthodontic tooth movement in acute and chronic corticosteroid treatment*

OBJECTIVES

To study tissue reaction to orthodontic loading during the course of short- and long-term corticosteroid administration.

DESIGN

'Split-mouth' design to perform orthodontic tooth movement in 64 six-month-old male rats divided into groups: no drug administration (n = 19), acute (n = 22) and chronic (n = 23) 8 mg/kg/day corticosteroid treatment. Performed in the Department of Orthodontics at Aarhus University.

EXPERIMENTAL VARIABLE

The upper left first molar was moved for 21 days. Bone markers were administered at 7 and 2 days before sacrifice. Histological sections were cut at the coronal level.

OUTCOME MEASURE

Tooth movement rate, alveolar socket area, the relative extension of alveolar wall with erosion, and the mineralizing surfaces were measured and compared in the three groups.

RESULTS

Tooth movement rate increased in the chronic group. The mechanical load induced an enlargement of the alveolar wall that was less pronounced in both medicated groups. In the acute group the drug suppressed bone resorption and formation without mechanical stimulus. Force application resulted in significant increase in the relative extension of resorption and formation in both drug groups; it was particularly pronounced in the chronic group.

CONCLUSION

Because acute corticosteroid ingestion reduces bone turnover, in these patients orthodontic treatment might best be postponed until a time the patient is free of the drug. Chronic steroid ingestion leads to an increased biological reaction to mechanical perturbation indicating that the orthodontic force level should be reduced and controlled more frequently in patients on chronic steroid treatment.

Tissue reaction to orthodontic tooth movement in different bone turnover conditions

OBJECTIVES

To study the tissue reaction to orthodontic load in normal, high, and low bone turnover states.

DESIGN

'Split mouth' design performing orthodontic tooth movement in 52, 6-month-old male rats with: normal (n = 19), high (n = 16), and low bone turnover (n = 17), the latter two being obtained by induction of hyperthyroidism and hypothyroidism, respectively. Performed at the Department of Orthodontics at Aarhus University.

EXPERIMENTAL VARIABLE

The upper left first molar was moved for 21 days. Bone markers were administered 7 and 2 days before killing. Histological sections were cut at the coronal and apical levels.

OUTCOME MEASURE

Alveolar socket area, periodontal ligament width, the relative extension of alveolar wall with erosion surfaces, and the mineralizing surfaces were measured and compared in the three groups.

RESULTS

Alveolar socket, periodontal ligament width, and erosion surface were larger on the treated than on the control side in the three groups. The normal and hypothyroid groups showed a wider periodontal ligament at the bucco-distal site at the coronal level, while the hyperthyroid group showed a widening which was not spatially oriented. The normal and hyperthyroid groups showed higher erosion at the corono-mesial site. The mineralizing surfaces were larger on the treated than on the control side in the normal and hypothyroid groups, but not in the hyperthyroid group.

CONCLUSION

In the hyperthyroid group, the widening of the periodontal ligament was not spatially oriented and the increased erosion was not accompanied by increased formation, as observed in the normal and hypothyroid groups.

Combined apexification and orthodontic intrusion of a traumatically extruded immature permanent incisor

A patient with a traumatic extrusion of the maxillary right central incisor was referred to the Pedodontic Clinic of Gazi University Faculty of Dentistry after 15 days. Orthodontic repositioning of the tooth was planned in 6 months. At the beginning of orthodontic therapy it was observed that the tooth was necrotic and needed an apexification procedure. The apexification procedure and orthodontic intrusion were successfully performed at the same time. In addition, a "walking bleach" was performed after the orthodontic and endodontic procedures were completed. At the 3-year recall, the tooth appeared normal in all respects.

Osteoclast clearance from periodontal tissues during orthodontic tooth movement

The presence of osteoclasts at locations of alveolar bone remodeling is antecedent to orthodontic tooth movement. Cell recruitment and clearance are the mechanisms by which osteoclast populations are regulated. Research in other tissues has revealed that many cells die after their functional lives are past by a process called apoptosis, or programmed cell death. The purpose of this study was to examine the role of apoptosis in osteoclast clearance at orthodontically treated sites as a function of time and location. Orthodontic appliances were placed on 96 rats of the Sprague-Dawley strain. The rats were assigned to either treatment or sham (control) groups and killed 1, 3, 5, and 7 days after appliance placement. Tissue samples were prepared for histochemical evaluation and quantification of morphologic features. Tartrate-resistant acid phosphatase (TRAP) and ApopTag (TdT-mediated dUTP-biotin nick 3' end labeling) stains were used to identify osteoclasts and committed preosteoclasts and to discriminate between apoptotic and nonapoptotic nuclei. Pyknotic nuclei and apoptotic bodies were also counted as a morphologic assessment of apoptosis. The percentages of TRAP/ApopTag-positive nuclei were measured in 4 different periodontal regions. There was a highly significant difference in the overall percentage of TRAP/ApopTag-positive nuclei between the control and the treatment groups at 3, 5, and 7 days (P <.001). Morphologic criteria were also statistically different at days 5 and 7 (P <.05). These data strongly suggested that osteoclasts recruited for orthodontic tooth movement are, at least in part, cleared by apoptosis.

Intrusion of overerupted molars by corticotomy and magnets

Although posterior tooth intrusion in an adult patient is a difficult procedure, it can be achieved without extruding the adjacent teeth by performing a corticotomy and using magnets. In carrying out this procedure on 2 adult patients whose molars had overerupted due to the early loss of antagonists, tooth movement was rapidly achieved without discomfort or side effects.

Rapid orthodontic tooth movement into newly distracted bone after mandibular distraction osteogenesis in a canine model

Orthodontic tooth movement through recently distracted fibrous bone tissue has not been investigated previously. We hypothesized that a tooth can be moved into the fibrous new bone created by the distraction process at a rapid rate. Four mature beagle dogs were used in this study. An edentulous space was created in 2 weeks by using a bone-borne intraoral distraction device on each side of the mandibular body between the third and fourth premolars. Calibrated elastic threads with 50 g of orthodontic force were applied to move the fourth premolar into the edentulous space for 5 weeks. On one side, the tooth was moved simultaneously with distraction; and on the opposite side, it was initiated immediately after the cessation of distraction. The fourth premolars were moved 1.2 mm per week. The results indicated that the best time to initiate tooth movement was immediately after the end of distraction. With this approach, most of the periodontal support was preserved after orthodontic tooth movement. In contrast, moderate to severe alveolar bone loss was noted in the fourth premolars moved simultaneously with distraction. This is one of the first experimental studies to demonstrate successful rapid orthodontic tooth movement into an edentulous space newly created by distraction osteogenesis. Clinical implications of these results may be applied to relieve severe dental crowding and to correct sagittal or transverse dental arch discrepancies.

Later orthodontic appliance reactivation stimulates immediate appearance of osteoclasts and linear tooth movement

BACKGROUND

Delays in the appearance of osteoclasts at compression sites occur after orthodontic appliance reactivation, when this is done during both the period of osteoclast recruitment and the peak expansion in the osteoclast population. This experiment examines osteoclasts and tooth movement in alveolar bone after appliance reactivation coinciding with alveolar bone formation and the time when reactivation osteoclasts first appear (ie, 10 days after initial appliance activation).

METHODS

Bilateral orthodontic appliances were activated to mesially tip maxillary molars with 40 cN in 144 rats. After 10 days, all rats were randomized into two groups of 72. Group I had appliances reactivated in precisely the same manner as the first activation. Group II had appliances sham-reactivated. Nine to 12 rats were then sacrificed at 1, 3, 5, 7, 10, and 14 days in both groups (eg, day 1 represents an interval of 11 days after the first appliance activation and 1 day after either sham or real reactivation). Orthodontic movement was measured cephalometrically; changes in osteoclasts and root resorption were assessed at both compression and tension sites histomorphometrically.

RESULTS

Teeth in the reactivated group (Group I) displayed linear tooth movement (62.6 micrometers/day), and 0.9 mm tooth movement by day 10. Significant increases in osteoclast numbers, osteoclast surface percentage, and surface per individual osteoclast were evident in these animals by 1 day postreactivation (P <.01). Significant treatment-related increases in root resorption were not evident at compression sites at any time.

CONCLUSIONS

These findings indicate that, after appliance reactivation during the time when reactivation osteoclasts appear, a second cohort of osteoclasts can be recruited immediately, along with immediate and substantial tooth movement and no greater risk of root resorption.

Rapid canine retraction through distraction of the periodontal ligament

The process of osteogenesis in the periodontal ligament during orthodontic tooth movement is similar to the osteogenesis in the midpalatal suture during rapid palatal expansion. A new concept of "distracting the periodontal ligament" is proposed to elicit rapid canine retraction in 3 weeks. It is called dental distraction. Fifteen orthodontic patients (26 canines, including 15 uppers and 11 lowers) who needed canine retraction and first premolar extraction were included. At the time of first premolar extraction, the interseptal bone distal to the canine was undermined with a bone bur, grooving vertically inside the extraction socket along the buccal and lingual sides and extending obliquely toward the socket base. Then, a tooth-borne, custom-made, intraoral distraction device was placed to distract the canine distally into the extraction space. It was activated 0.5 to 1.0 mm/day immediately after the extraction. The anchor units were the second premolar and first molar. Cephalometric and periapical x-rays were taken before and after the canine retraction. Both the upper and lower canines were distracted bodily 6.5 mm into the extraction space within 3 weeks. New alveolar bone was generated and remodeled rapidly in the mesial periodontal ligament of the canine during and after the distraction. It became mature and indistinguishable from the native alveolar bone 3 months after distraction. During the distraction, 73% of the first molars did not move mesially and 27% of them moved less than 0.5 mm mesially within 3 weeks. The radiographic examination revealed that apical or lateral surface root resorption of the canine was minimal. No periodontal defect or endodontic lesion was observed throughout and after distraction. We concluded that the periodontal ligament could be rapidly distracted without complications. The rapid orthodontic tooth movement through distracting the periodontal ligament cannot be emulated by current conventional orthodontic concepts and methods.

Radiographic evaluation of apical root resorption with 2 different types of edgewise appliances. Results of a randomized clinical trial

The purpose of this paper was to compare radiographically the prevalence and degree of apical root resorption after treatment with a fully programmed edgewise appliance (FPA) and a partly programmed edgewise appliance (PPA) in a randomized multipractice clinical trial. Two groups of patients with Class II malocclusions were treated orthodontically. The type of treatment was randomly assigned by a computer program. During fixed appliance therapy, one group was treated according to the precepts of the straight wire concept (FPA; n = 32) while the other was treated with conventional full edgewise mechanics (PPA; n = 29). Treatment times were recorded. Radiographs of the maxillary incisors were made before and after active treatment with fixed appliances using the bisecting angle technique. To correct for different projecting angles the pairs of radiographs were digitally reconstructed. The prevalence and degree of root resorption were assessed. The mean treatment time was 1.8 years and 1.6 years for treatment with FPA and PPA, respectively. The mean amount of loss of tooth length was 8.2% for the patients treated with FPA and 7.5% for the patients treated with PPA. No statistically significant differences could be assessed between both groups at the end of active treatment. The mean prevalence of apical root resorption was 75% for the patients treated with FPA and 55% for the patients treated with PPA. Statistical evaluation showed no significant differences. We concluded that the prevalence and degree of root resorption is independent of the appliances as used in this study.

Effect of orthodontic appliance reactivation during the period of peak expansion in the osteoclast population

BACKGROUND

Delays in the appearance ofosteoclasts at compression sites occur following orthodontic appliance reactivation when this is done during the period of osteoclast recruitment. This study examined changes in alveolar bone after appliance reactivation at a time coinciding with the peak expansion of the osteoclast population following the first appliance activation.

METHODS

Orthodontic appliances were activated with 40 g on maxillary molars followed by a reactivation with the same force after 4 days in one group and sham reactivation in the other. Rats were killed at 0, 1, 3, 6, and 10 days thereafter. Orthodontic movement was measured cephalometrically. TRAP and interleukin-1 alpha (IL-1alpha) were measured biochemically, and changes in osteoclasts and root resorption were assessed at both compression and tension sites histomorphometrically.

RESULTS

Teeth in the reactivated group displayed more initial displacement than controls but no more tooth movement 10 days following appliance reactivation. Also, increases in osteoclast numbers and surface percent, as well as alveolar bone Tartrate-resistant acid phosphatase (TRAP), became evident in the treated animals only 10 days after reactivation. However, IL-1alpha was elevated in alveolar bone within 1 hr following appliance reactivation but returned to baseline by day 1. There were no treatment-related difference in nuclear number per osteoclast or trabecular surface per osteoclast. Significant treatment-related increases in root resorption were evident at compression sites by day 10.

CONCLUSIONS

These findings indicate that after appliance reactivation during the height of osteoclastic stimulation, a second cohort of osteoclasts can be recruited, but only after a delay of several days. This delay is not due to a failure to produce IL-1alpha in the tissues.

Histomorphometric and biochemical study of osteoclasts at orthodontic compression sites in the rat during indomethacin inhibition

Prostaglandins affect the number of osteoclasts at compression sites in orthodontic tooth movement. They may also have a role in tooth movement and influence the extent of root resorption. The purpose was to examine the effect of indomethacin on the activity of resident osteoclasts, recruitment of new osteoclasts and root resorption at orthodontic compression sites. Two separate populations of osteoclasts were studied: those resident at the sites after initial appliance activation and those recruited by a subsequent activation. Orthodontic appliances were activated to provide mesially directed forces of 40 g on the maxillary molars of rats. The appliances were activated with the same force after 4 days. The rats were killed at 1, 3, 6 and 10 days after initial activation. Half of the rats were injected with indomethacin. Tooth movement was measured cephalometrically; osteoclast numbers, sizes, numbers of nuclei per osteoclast and root resorption were assessed histomorphometrically; tartrate-resistant acid phosphatase (TRAP) in alveolar bone was measured biochemically. Indomethacin inhibited both initial tooth displacement and that following the delay. It also reduced the increase in osteoclast numbers, total osteoclast surface and alveolar bone TRAP at day 10. It had no effect on the surface area of each individual osteoclast or number of nuclei in each osteoclast. Root resorption increased in both groups but it was enhanced at day 10 in the indomethacin group. These data suggest that orthodontic tooth movement after appliance activation requires the recruitment of osteoclasts to sites of compression and that this is indomethacin-sensitive. Furthermore, indomethacin enhances root resorption at compression sites 10 days after appliance reactivation.

Orthodontically induced root resorption in rat molars after 1-hydroxyethylidene-1,1-bisphosphonate injection

A single injection of 1-hydroxyethylidene-1, 1-bisphosphonate inhibits the formation of acellular cementum in rat molars. Instead, an atypical hyperplastic cementum is formed. In this study the resistance of this cementum to resorption was tested by applying an orthodontic force. It was found that roots lacking acellular cementum were readily resorbed. The readiness with which the atypical hyperplastic cementum was resorbed without any increase in multinucleated osteoblasts may offer useful opportunities to study the different phases of hard-tissue resorption.

A radiographic comparison of apical root resorption after orthodontic treatment with the edgewise and Speed appliances

Apical root resorption is a serious iatrogenic problem sometimes associated with orthodontic treatment. The Speed appliance (Strite Industries, Ltd., Ontario, Canada) provides a continuous rotatory and torque action through its spring clip mechanism, in contrast with the edgewise appliance that may provide an interrupted force. The effect of continuous action on root resorption compared with the interrupted action of the edgewise system has not been investigated previously. The purpose of the present investigation is to test the null hypothesis that there is no difference in the apical root resorption seen after orthodontic treatment with the edgewise straight wire and the Speed appliance systems. Pretreatment and posttreatment periapical radiographs of 63 patients, (30 treated with the Speed 0.018 bracket and 33 with the 0.018 edgewise bracket) were studied. The long cone paralleling technique was used for all the radiographs. Any image distortion between the pretreatment and posttreatment radiograph was calculated and compensated for by using the crown length measurements, on the assumption that the crown length remains unaltered during the treatment period. Quantitative measurements of crown and root lengths for the maxillary and the mandibular central and lateral incisors were compared. Means and standard deviations for the percentage root resorption per tooth group were calculated. A three-factor analysis for variance (ANOVA test) was performed to determine whether there was an appliance, treatment, or gender effect on the amount of root resorption seen after treatment. No statistically significant difference in root resorption between the two appliance systems was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair processes in the periodontium following dentoalveolar ankylosis: the effect of masticatory function

It has recently been shown that administration of the drug 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) perturbs the homeostasis in the periodontal ligament resulting in an osteoid-mediated ankylosis between the alveolar wall and the root surface. In the present study, the events after discontinuing HEBP administration were investigated and the effect of function on repair of the periodontal ligament was evaluated. In mice, the maxillary left molars were extracted. They then received a daily subcutaneous injection of HEBP (10 mg P/kg b.w.) for a period of 50 days, were killed 24 h, 14, 28, 56 and 112 days after the last injection and their mandibles processed for light microscopy. HEBP administration caused a significant decrease of the width of the periodontal ligament space with localized ankylosis. In the period after discontinuing HEBP treatment, the newly-formed bone did first mineralize and was then partly resorbed resulting in the disappearance of the ankylotic areas. Furthermore, root resorption was seen. Finally, the periodontal ligament regained its normal architecture and width and a new layer of cementum was formed. Functional teeth showed more root resorption than hypofunctional ones and a more rapid repair of the periodontal ligament. It is concluded that in the period after HEBP treatment the periodontal ligament regains its normal width by a repair process including extensive root resorption, that seems to accelerate this process.

Apical root resorption in orthodontically treated subjects: analysis of edgewise and light wire mechanics

Of the several modes of tooth movement, pressure from intrusive forces seems the most likely to cause external apical root resorption (EARR). This has been demonstrated for incisors in human beings and molars in laboratory animals. The present study examined full-banded adolescent patients and scored the degrees of in-treatment root resorption throughout the dentition. Just Class I cases with four first premolar extractions were used. Equal samples of conventional Begg and Tweed treated cases were examined with 1:1 sex ratios (total n = 83). No difference between the Begg and Tweed techniques and no sex difference was found in any of the 30 univariate tests, even though power analysis indicated a strong likelihood of finding a difference if one existed. By using multiple linear regression, significant decreases in length (EARR) were found for those roots systematically intruded in this Class I malocclusion, notably the mesial root of the maxillary first molar and the distal root of the mandibular first molar. Even though some of the present cases had been in "active" treatment up to 6 years, we found no significant association between duration of treatment and degree or amount of EARR.

Traumatic root resorption in dentine-immunized mice

Traumatic root resorption in a mouse model has been shown to coincide with a decline in naturally occurring serum antibody levels to dentin. It has been proposed that root resorption may be dentin antibody mediated. The purpose of this study was to examine the traumatic root resorption response in mice after hyperimmunization with a crude tooth extract (dentin). The hypothesis of this study was that elevated dentin antibody titers would positively correlate with root resorption. Mice were immunized with mouse dentin and controls were sham immunized. All mice were boosted 4 weeks later with or without mouse dentin as appropriate. All mice were then boosted two more times at weekly intervals with mouse dentin and then twice at weekly intervals with rat dentin. The change to rat dentin was made to increase mouse serum antibody titers to dentin. Serum samples were obtained before the initial immunization and weekly after each boost and were examined for antibody-to-dentin antigen by the enzyme-linked immune sorbent assay (ELISA). One week after the second boost with rat dentin, all animals were exposed to the cryoprobe procedure. Mice were killed 10 days later, and serum tested for antibody to dentin antigen. The incisors were examined by scanning electron microscopy, and root resorption quantified. Root resorption was observed on the incisors in the sham-immunized mice but not in the dentin-immunized mice. A trend toward increased serum antibody titers to dentin in immunized mice was observed over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Root resorption after orthodontic treatment: Part 2. Literature review

All permanent teeth may show microscopic amounts of root resorption that are clinically insignificant and radiographically undetected. Root resorption of permanent teeth is a probable consequence of orthodontic treatment and active tooth movement. The incidence of reported root resorption during orthodontic treatment varies widely among investigators. Usually, extensive resorption does not affect the functional capacity or the effective life of the tooth. Most studies agree that the root resorption process ceases once the active treatment is terminated. Root resorption of the deciduous dentition is a normal, essential, and physiologic process. Permanent teeth have the potential to clinically undergo significant external root resorption when affected by several stimuli. This resorptive potential varies in persons and between different teeth in the same person. This throws doubt on the role of systemic factors as a primary cause of root resorption during orthodontic treatment. Tooth structure, alveolar bone structure at various locations, and types of movement may explain these variations. The extent of treatment duration and mechanical factors definitely influence root resorption. In most root resorption studies, it is not possible to compare the results and conclusions because of their different methods. Further research in this field is necessary to advance the service of the specialty. The question of whether there is an optimal force to move teeth without resorption or whether root resorption may be predictable remain unanswered. This review indicates the unpredictability and widespread incidence of the root resorption phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair process of external root resorption subsequent to palatal expansion treatment

The repair process of external root resorption (ERR) and the role of retention mechanics in enhancing ERR repair were studied on eight Macaca fascicularis monkeys that were divided equally into short- and long-term groups. Six monkeys received palatal expansion appliances, and two received sham appliances. The short-term group received active treatment. The long-term group received additional retention (4 months) and relapse (2 months) treatment periods with biweekly injections of individual vital dye per phase, i.e., procion red H-8B and violet H-3R (80 mg/kg B.W.), respectively. Histomorphologic examinations included scanning electron microscopy, light, and ultraviolet microscopy. The short-term group demonstrated penetrated resorption with pulp exposure at sites with initial deficiency of the protecting odontoblastic layer (apical zone, nutrition canal). The long-term group showed two forms of ERR repair: (1) Nonfunctional retarded repair cementum, comprised of overlapped incremental lines and deprived of extrinsic fibers, was delineated in severe pulp exposure. The pulp/dentin complex showed intense incorporation of procion dye in the dentinal tubuli, conceivably related to a defense response in the form of sclerotic dentin. (2) Functional rapid repair cementum, comprised of discriminated incremental lines mainly of mixed cellular cementum, with a consistent pattern of five sequential phases: the lag phase (14 to 28 days), the incipient phase (14 days), the peak phase (14 to 28 days), the steady phase (42 to 56 days) and the retreating phase (70 days). Sharpey's fibers at functional ERR sites were scarce, never emerging from the dentinocemental junction, and not developing into principal fibers. The pulp/dentin complex showed an increase in pulp stones but no formation of tertiary dentin. The apical area responded by hypercementosis in the form of apical occlusion and a displaced pulp canal. The application of a fixed retention device is recommended in light of accelerated apposition of repair cementum during the retention period. However, increased formation of Sharpey's fibers during the relapse period might suggest a restricted duration in splinting therapy.

Tooth movement

This article reviews the evolution of concepts regarding the biological foundation of force-induced tooth movement. Nineteenth century hypotheses proposed two mechanisms: application of pressure and tension to the periodontal ligament (PDL), and bending of the alveolar bone. Histologic investigations in the early and middle years of the 20th century revealed that both phenomena actually occur concomitantly, and that cells, as well as extracellular components of the PDL and alveolar bone, participate in the response to applied mechanical forces, which ultimately results in remodeling activities. Experiments with isolated cells in culture demonstrated that shape distortion might lead to cellular activation, either by opening plasma membrane ion channels, or by crystallizing cytoskeletal filaments. Mechanical distortion of collagenous matrices, mineralized or non-mineralized, may, on the other hand, evoke the development of bioelectric phenomena (stress-generated potentials and streaming potentials) that are capable of stimulating cells by altering the electric charge on their membrane or their fluid envelope. In intact animals, mechanical perturbations on the order of about 1 min/d are apparently sufficient to cause profound osteogenic responses, perhaps due to matrix proteoglycan-related "strain memory". Enzymatically isolated human PDL cells respond biochemically to mechanical and chemical signals. The latter include endocrines, autocrines, and paracrines. Histochemical and immunohistochemical studies showed that during the early places of tooth movement, PDL fluids are shifted, and cells and matrix are distorted. Vasoactive neurotransmitters are released from periodontal nerve terminals, causing leukocytes to migrate out of adjacent capillaries. Cytokines and growth factors are secreted by these cells, stimulating PDL cells and alveolar bone lining cells to remodel their related matrices. This remodeling activity facilitates movement of teeth into areas in which bone had been resorbed. This emerging information suggests that in the living mammal, many cell types are involved in the biological response to applied mechanical stress to teeth, and thereby to bone. Essentially, cells of the nervous, immune, and endocrine systems become involved in the activation and response of PDL and alveolar bone cells to applied stresses. This fact implies that research in the area of the biological response to force application to teeth should be sufficiently broad to include explorations of possible associations between physical, cellular, and molecular phenomena. The goals of this investigative field should continue to expound on fundamental principles, particularly on extrapolating new findings to the clinical environment, where millions of patients are subjected annually to applications of mechanical forces to their teeth for long periods of time in an effort to improve their position in the oral cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

[The causes of and repair procedures in external root resorption following palatal suture expansion with magnetic and conventional dilators. Experimental animal research on Macaca fascicularis monkeys]

Eight Macaca fascicularis monkeys received rapid maxillary expansion with conventional and magnetic appliances. The histomorphometric analysis (SEM) showed increased external root resorption (ERR) in: multirooted teeth, buccal root surfaces, mesiobuccal roots and apical zones. ERR is determined by the impulse, the decrease in the periodontal width and the extent of mineralization of adjacent hard tissues. The microscopic examinations of light, UV and SEM defined two types of cellular cement in ERR areas: a) unfunctional repair cement (slow type), b) functional repair cement (rapid type). The first was characterized by the absence of Sharpey's fibers and by overlapped incremental lines, the second by the formation of new Sharpey's fibers and discriminated incremental lines. These incremental lines indicate five sequential phases with diverse rates of cement apposition, i.e. lag-, incipient-, peak-, steady-, and retreating phase. Therefore, the study recommends the application of a fixed retainer immediately subsequent to rapid maxillary expansion which is followed by an intermittent retention appliance.